<p>Checks the header of a source file against a header that contains a regular expression for each line of the source header.</p>
<p>Rationale: In some projects checking against a fixed header is not sufficient, e.g. the header might require a copyright line where the year information is not static. For example, consider the following header:</p>
<pre>
    line  1: ^/{71}$
    line  2: ^// checkstyle:$
    line  3: ^// Checks Java source code for adherence to a set of rules\.$
    line  4: ^// Copyright \(C\) \d\d\d\d  Oliver Burn$
    line  5: ^// Last modification by \$Author.*\$$
    line  6: ^/{71}$
    line  7:
    line  8: ^package
    line  9:
    line 10: ^import
    line 11:
    line 12: ^/\*\*
    line 13: ^ \*([^/]|$)
    line 14: ^ \*/
</pre>
<p>Lines 1 and 6 demonstrate a more compact notation for 71 '/' characters. Line 4 enforces that the copyright notice includes a four digit year. Line 5 is an example how to enforce revision control keywords in a file header. Lines 12-14 is a template for javadoc (line 13 is so complicated to remove conflict with and of javadoc comment).</p>
<p>Different programming languages have different comment syntax rules, but all of them start a comment with a non-word character. Hence you can often use the non-word character class to abstract away the concrete comment syntax and allow checking the header for different languages with a single header definition. For example, consider the following header specification (note that this is not the full Apache license header):</p>
<pre>
    line 1: ^#!
    line 2: ^&lt;\?xml.*&gt;$
    line 3: ^\W*$
    line 4: ^\W*Copyright 2006 The Apache Software Foundation or its licensors, as applicable\.$
    line 5: ^\W*Licensed under the Apache License, Version 2\.0 \(the "License"\);$
    line 6: ^\W*$
</pre>
<p>Lines 1 and 2 leave room for technical header lines, e.g. the "#!/bin/sh" line in Unix shell scripts, or the xml file header of XML files. Set the multiline property to "1, 2" so these lines can be ignored for file types where they do no apply. Lines 3 through 6 define the actual header content. Note how lines 2, 4 and 5 use escapes for characters that have special regexp semantics.</p>
<p>Note: ignoreLines property has been removed from this check to simplify it. To make some line optional use "^.*$" regexp for this line. </p>

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